This disclosure relates to microfluidic devices for sample preparation, processing, purification, and extraction with a solid phase.
Most samples that are collected for diagnostic testing are complex mixtures of analytes and matrix. In many cases, the matrix includes many undesirable constituents that can interfere with analysis. Complicating matters further, analytes are often present at very low concentrations relative to the highly abundant matrix constituents. Thus, a critical step in many applications is sample preparation, isolation and extraction.
In many assay protocols, the analyte must first be separated from the matrix and often concentrated prior to analysis. The most common method for sample preparation is solid phase extraction (SPE), which exploits interactions between a liquid sample and a solid stationary phase material (often formed from a packed bed of beads or a porous polymer monolith). When a liquid sample is passed over or through the stationary phase, analyte is retained on the solid phase while matrix compounds are washed away. Traditionally, the stationary phase is hydrophobic (similar to reversed-phase media for chromatography), which facilitates purification of non-polar analytes from polar constituents. After washing the solid phase, analyte retained within the solid phase may be eluted in a different solvent (which has high affinity for the analytes), which may have a volume that is smaller than the initial sample volume, thereby concentrating the extracted analyte. The purified sample is then ready for analysis.
Although SPE is ubiquitous for sample preparation using macroscale protocols and systems, SPE has recently been applied to microchannels to take advantage of the high surface-to-volume ratios and short diffusion distances exhibited within microchannels. The microchannel-based SPE techniques reported previously have employed solid-phase materials formed directly on channel walls,1, 2 from packed beds of beads,3-10 from porous membranes,11-14 and from porous polymer monoliths (PPM).15, 16 
Despite these developments, the microchannel-based SPE methods reported previously are not useful for some applications. For example, such methods are typically not amenable to preparative-scale applications, because samples handled in microchannels may be difficult to recover.